1. Field of the Invention
The present invention relates to ink-jet printers generally and, more particularly, to processes and apparatus for spraying ink from the chamber for the head of an ink jet printer and onto a printable medium.
2. Discussion of Related Art
Typically, conventional ink-jet printers include a central processing unit that is driven by signals received from a host computer through printer interface, to read a system program from memory, to store values initially set for the printing operation and various information necessary for the printing system, and to then execute the system program to produce a control signal; a read only memory that holds programs for controlling the printer; and a random access memory that temporarily stores data for operation of the system. An application-specification integrated circuit transmits data from the central processing unit to most of the peripheral logic ASICs as may be necessary to execute the instructions from the central processing unit, a head driver 30 that controls the operation of ink cartridge in response to an output control signal from the central processing unit, a maintenance motor driving circuit that serves to drive a maintenance motor and prevent the nozzle of ink cartridge from being exposed to air, a carriage motor driving circuit that controls the operation of a carriage return driving motor, and a line feed motor driving circuit which controls the operation of a line feed motor to feed paper to a top output tray by using a stepping motor. A print signal, transmitted to the print interface from the host computer, actuates these motors in response to control signals from the central processing unit during performance of the printing operation. The ink cartridge sprays small drops of ink on paper through a plurality of orifices in a nozzle to form characters on the paper in a dot-matrix format.
The ink cartridge includes ink absorbed by a sponge held in a case, and an ink-jet printer head constructed with a filter to remove impurities from the ink, an ink stand pipe chamber storing ink that is filtered by the filter, an ink via hole supplying a chip containing ink heating portions and ink chambers, with the ink delivered through a stand pipe chamber, and a nozzle plate having a plurality of orifices for expelling the ink, transmitted from ink via hole. The ink via provides ink to the ink chambers between the nozzle plate and chip, a plurality of ink channels transmit the ink to each
orifice of the nozzle plate from the ink via hole, ink chambers that spray the ink supplied from ink channels, and a plurality of electrical connectors that furnish electrical power to the ink chambers.
The ink-jet printer head includes a resistor layer that is formed over a silicon oxide film created on a silicon substrate, for heating the ink with the electric energy. Two electrode layers are formed over resistor layer. Multi-layer protective layers prevent heating portions created between the two electrodes and resistor layer from being eroded and deformed by chemical interaction with the ink. The ink-jet chambers produce ink bubbles in the ink with the heat generated by the heating portions. Ink-jet printer head is typically constructed with ink channels that serve as a passage for leading the ink from ink via holes into ink chambers. Ink barriers serve as a wall to form a space used for leading the ink from the ink channels into ink chambers. A nozzle plate contains a plurality of orifices through which every ink particle, pushed according to its volume change, is sprayed onto the print media.
Nozzle plate and heating portions are spaced a predetermined distance away from each other for mutual correspondence. The pair of electrodes are connected with a bumper for electrical connection. This bumper is electrically connected with a head controller so that the ink particles can be sprayed through each orifice of the nozzle. Each ink barrier is formed to lead the ink from the side of heating portions, and is connected with common ink via to direct the ink flow out of an ink container. A head driver furnishes electric energy to a pair of electrodes in response to a control instruction of that receives a command to print through the printer interface. The power is transmitted through the two electrodes to heat heating portions by the heat of electrical resistance, i.e. joule heat (P=I.sup.2 R) for a predetermined period of time. The top surface of the heating portions are heated to 500.degree. C..about.550.degree. C. to transmit the heat to multi-layer protective layers. The heat is transmitted to the ink particles spreading across the protective layers. More ink bubbles are produced by the steam pressure in the middle of the heating portions than in any other area, and the highest steam pressure is created in the middle of the heating portions. The ink bubbles, produced by this heat, cause a change in the volume of the ink on the top of the heating portions. Ink particles that are pushed as the volume of ink is changed, are jetted out through the orifices of nozzle plate.
If the electric energy, furnished to two electrodes is cut off, the heating portions cool instantaneously, and the ink bubbles are deflated and the ink returns to its original state. The ink particles, discharged to the outside, are sprayed on paper in the shape of small drops by surface tension, thus forming characters on paper in a dot-matrix format. The ink chamber's internal pressure drops according to the change in the bubble volume, and the ink from the ink container refills nozzle plate through the ink via hole.
I have noticed that the conventional ink spraying mechanism, using the conventional ink-jet printer head, has the following disadvantages. First, when forming bubbles with the super-heat so as to spray the ink onto print media, the composition of the ink may be changed by the heat, and a shock wave, created by the generation and breaking of the ink bubbles, deleteriously affects the internal components of the head, with a concomitant reduction in performance and print quality.
Second, as the ink adheres to the resistor layer and the two electrodes, the ink interacts electrically with the two electrodes, and, accordingly, corrosion occurs by ion exchange at each boundary layer of the heating portions and two electrodes, thus reducing the operational life of the head.
Third, the shock wave, created by the generation of ink bubbles in ink barrier containing the ink, causes an increase in the refresh cycle time.
Fourth, the ink drop's straight-forwardness and roundness, and the uniformity in the amount of ink discharged--all of which affect the print quality--depend on the shape of the ink drop. The manufacturing process becomes complicated, thereby increasing the production costs as the multilayer protective layers are formed over the electrodes and resistor layer.
Recent efforts to solve these problems include the formation of first and second electrodes on and under a nozzle plate, with a nozzle being formed by using an eximer laser. The nozzle is directly connected to an ink container to introduce conductive ink into the nozzle by using capillarity. High voltages are applied to the two electrodes to heat and evaporate the conductive ink inside the nozzle. The steam pressure, generated during this process, causes the ink particles inside the nozzle to be sprayed onto the print media. The upper section of the nozzle is larger than the lower section, and the voltage applied to each electrode is about 1000 Volts.about.3000 Volts at a frequency of up to 10 kiloHertz.
I have noticed however, that with this improved technique, as the ink inside nozzle is heated by the high voltage to be sprayed on the paper, the length of nozzle should necessarily be long. A hole in the electrode connected with the nozzle is larger than a cross-sectional area of the nozzle's lower section. Thus, when the voltage is applied to each electrode, it is difficult to achieve a concentration of electric current density that is satisfactory, thus necessarily requiring high voltages. The nozzle plate, having two electrodes and a nozzle, must be formed thick, and the time required to manufacture nozzle plate is long, thus increasing the overall production costs.